oldlady Posted May 30, 2017 Report Share Posted May 30, 2017 several of my shelves have warped. i need them flat because making flat things demands that they do not rock when placed on a table. most are ok but i have a photo of one shelf that is about 1/4 inch down in the center. the second is about 1/8 inch. i will be firing to cone 6 in a few days and hope to be able to turn these 2 shelves upside down and hope the sag is reduced. is there a special spot in the kiln where the effect will be more likely to happen? i assume the hottest location is best but that is at the top. should i weigh down the shelf that needs straightening with a flat one? being unable to "waste" a firing on just this, i plan to load the rest of the kiln with glazed ware. do you think it can be done? Link to comment Share on other sites More sharing options...
Marcia Selsor Posted May 30, 2017 Report Share Posted May 30, 2017 I would try filling the sag with some grog and level it. maybe before you even put it in the kiln. If they aren't cracked, just live with it. I would be cautious of flipping them they could crack from that. marcia Link to comment Share on other sites More sharing options...
neilestrick Posted May 30, 2017 Report Share Posted May 30, 2017 I don't think it'll crack, but it will take a lot more than one firing to get it to flatten back out, and even then it may not flatten out. And you'll have to grind all the wash off before flipping. It's often easier to buy new shelves. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted May 30, 2017 Report Share Posted May 30, 2017 that should have said GROG...must have auto corrected. Marcia Link to comment Share on other sites More sharing options...
oldlady Posted May 30, 2017 Author Report Share Posted May 30, 2017 thanks, neil. the wallet says no new shelves. check the retail price and you might see why. it took years to get this bad, i guess one firing won't do much but i will try it. marcia, good idea, maybe silica sand and grog. you would be very surprised at what "corrections" have been made to all of your posts since you started the move last year. my inner proofreader just keeps popping up whenever i read anything so when yours ALL came up with strange things i started watching. maybe one or two have gotten by that were correct from the start. Link to comment Share on other sites More sharing options...
fergusonjeff Posted May 30, 2017 Report Share Posted May 30, 2017 I use usual solid electric kiln shelves (3/4" thick 26" half-round) in my 10 cubic foot kiln typically fired to cone 6. Using three stilts puts the long diameter side with only supports at the ends. They warp almost 1/2" within about 10-12 firings. I then remove the wash, flip, and re-wash. They do flatten back out, but only temporarily on their way to warping the other direction. No cracking from this yet. I recently purchased a couple of the hollow (core-light?) shelves and they have gone almost 10 firing and no warp at all. They are not much more that the solid shelves. Might have to start slowly replace all the solid shelves. Link to comment Share on other sites More sharing options...
bciskepottery Posted May 30, 2017 Report Share Posted May 30, 2017 You can use wadding . . . puts the small trays above the kiln shelf and allows for more even cooling. 50% EPK/50% alumina. I've started doing this on my trays and very seldom get any warping. Link to comment Share on other sites More sharing options...
neilestrick Posted May 31, 2017 Report Share Posted May 31, 2017 My 14x28 rectangle Core-Lite shelves have gone several hundred firings without any warping. Link to comment Share on other sites More sharing options...
fergusonjeff Posted May 31, 2017 Report Share Posted May 31, 2017 Thanks Neil. They seemed too good to be true so I only bought 2. Guess it is time to get some more. Link to comment Share on other sites More sharing options...
oldlady Posted May 31, 2017 Author Report Share Posted May 31, 2017 kiln went on at 1:30 with a newly cleaned shelf upside down and near the top of the kiln. i used marcia's suggestion of grog but did something else with it. when i started grinding off the kiln wash, from about 1995, i noticed how it had alligatored on the entire shelf. normally, i just take the old 6 inch grinding wheel from a stationary unit and slide it across the shelf, knocking off the bits. today i put some grog on the shelf and ground it from medium to fine. in the process knocking off much more of the kiln wash than i have ever managed before. a little work with an old chisel on the stuff near the edges and a damp sponge finished the job. thank you, marcia. i did put some silica sand on the other shelves that were not so bad and fired pots on them. this shelf went upside down above an empty shelf on 1 inch posts. a second set of 1 inch posts holds another shelf above it so nothing will fall into my work. i hope. Link to comment Share on other sites More sharing options...
oldlady Posted June 2, 2017 Author Report Share Posted June 2, 2017 opened the kiln. found no change in the shelf. except that it is now clean and ready to be used again. i will try using it on the reverse since i do not want the sag to touch the pots on the shelf below. i do pack tightly. marcia, i added silica sand to the other shelves to level them and it worked very well. thank you for the suggestion. working alone in a studio means nobody to bounce ideas off of but this forum is a great resource and i appreciate everyone who posts anything. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted June 2, 2017 Report Share Posted June 2, 2017 thanks, neil. the wallet says no new shelves. check the retail price and you might see why. it took years to get this bad, i guess one firing won't do much but i will try it. marcia, good idea, maybe silica sand and grog. you would be very surprised at what "corrections" have been made to all of your posts since you started the move last year. my inner proofreader just keeps popping up whenever i read anything so when yours ALL came up with strange things i started watching. maybe one or two have gotten by that were correct from the start. I agree. I always think of you when I go back and see errors to correct. Still out of likes. I am glad the move is done. Still unpacking but everything is here or trashed. It is good to let go. Downsizing is tough but rewarding. Marcia Link to comment Share on other sites More sharing options...
douglas Posted June 15, 2017 Report Share Posted June 15, 2017 Would adding a fourth post in the middle that is sagging work? This would wobble, but the weight of the shelve above pressing on the fulcrum of the post in the middle might push the shelf down faster. Link to comment Share on other sites More sharing options...
oldlady Posted June 15, 2017 Author Report Share Posted June 15, 2017 douglas, thank you but i would not want to try this. my shelf came out of the firing fine, i put new kiln wash on it and some medium grog to level it so pots will come out flat. i do not fire often so this will be the time to grind off old kiln wash and replace it for next season, starting in late july. Link to comment Share on other sites More sharing options...
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